Handling Unmarshall Error in BP (ICAN505)

I have exposed BP as Web service in ICAN505
I have Catch-all exception block in BP to catch all the
exceptions in BP. I want to handle the unmarshall exception if
the Soap request received is not in proper format. But when I
am sending the malformed SOAP request I can see the exception in
the logs but it is not getting caught in the BP. It seems that
it is not reaching the BP at all.
Any suggestions on how can I handle the Unmarshall exception.

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